In a wheel assembly including a wheel and a tire, a dynamic imbalance may exist during manufacturing, due to the difference point of mass center and dimensional center during manufacturing of tire and wheel; we can probably control only the dimensional center in molding the tire and CNC wheel but can not or impossible to control the mass center in the tire and wheel, so when the wheel is rotated, various defects will occur such as a vibration or a noise. Generally, the method to compensate for this imbalance the wheel is provided with a balance weight, Usually, there are two kinds of fixative method to the wheel, which are by clip-on the rim and adhesives method. It is a skill in the art of wheel balance weights.
A conventional balance weight includes a weight body made from lead (Pb) and a clip having an end, which is embedded in said weight body. The record of the history patent in this field is listed in the United States Patent Classification (UPC) 301/5.21 to 5.22 and the International Patent Classification (IPC) B60B 1/00, 13/00.
We concluded the conventional manufacturing method thereof are as followings:
Weight Body: The weight body may be made of lead (Pb) or zinc (Zn). The weight body is manufacturing by gravity casting or die-casting.
Clip: Clip is a hook for mounting the balance weight to a flange of a wheel. The clip may be made of spring steel. The clip is fixed to the weight body by embedding an end portion of the clip in the weight body when the weight body is cast.
Heat Treatment: To obtain an elastic characteristic, a specific heat treatment is applied to the clip before the end of the clip is cast in the weight body. Because the melting point of lead is low, the elastic characteristic of the clip obtained by the heat treatment is not degraded when the end of the clip is cast in the weight body.
Surface Treatment: Surface treatment for prevention of rust and galvanizing corrosion coating is applied to the clip.
Metal Casting: Applied the clip to the one of the half mold, close the mold to pour the melted metal to fill the cavity and embedded the clip in the position.
Riveting: Riveting is a process used to bonding two parts together by drilling a hole put the rivet set into the hole, drawing a pin needle out which having one end bigger then the sleeve cylinder to expand to lock the hole. In U.S. Pat. No. 2,122,065 Hume
Caulking: Caulking is a process used to seal the seams in wooden boats, in order to make them watertight, or to close up crevices in building against water, air, dust or insects. Caulking as a term has spread to the meaning the activity of closing up joints and gaps such as Enami Seiki machine or similar. In U.S. Pat. Nos. 6,250,721 and 6,238,005 used budded caulking in wheel balance weight.
Recently, there has been a trend to avoid the industrial use of heavy metals such as lead (Pb) for the purpose of environmental protection. Thus, the lead of the balance weight is apt to be substituted for other materials.
As an alternative materials from an industrial viewpoint, the materials which are considered such as iron or copper can be used, Those materials are inexpensive, environmentally friendly and have a relatively high density.
However, since those materials have a relatively high melting point, the following problems occurred with respect to manufacture of the weight body and to bond the clip to the weight body: First, in case of casting where an end of the clip is cast in the weight body, since the melting points of the clip and the weight body is close to each other, the elastic characteristic of the clip is degraded or deteriorated, and the effect of the casting is weakened. If heat treatment of the clip is conducted after the clip is cast with the weight body, the condition of the heat treatment is more series because heat to the clip will be absorbed by the weight body and the heat treatment will be accompany by an increase in cost. Second, in a case where a surface treatment is applied to the clip before the clip is cast with the weight body, the clip is exposed to a high temperature during casting and the heat-treated surface is degraded. Therefore, various limitations and more modifications of the manufacturing method will be necessary.
In order to solve those problems, the inventors have investigated manufacturing the weight body by cold forging and coupling the clip to the weight body by caulking, this caulking system uses no heat to bind two parts together by punch dies. It can be used for coated sheets, and work hardening can be reduced. The caulking in plastic processing supports high speed processing already.
However, there are the following problems with manufacturing the weight body by cold forging: First, by cold-forging the material to the shape-forming of the weight body requires a large pressing force and a large-sized press machine which increases the manufacturing costs. Second, it is difficult to form the material into the shape-forming of the weight body in one pressing step, a plurality of pressing steps will be necessary. These results are in a need for a plurality of sets of pressing dies, which also increases the manufacturing costs.
For the above-mentioned reasons, the cost of the balance weight will be high. Solutions for the cost problem are thus desired.
U.S. Pat. No. 6,238,005 try solving by manufacturing the weight body by engaging groove of said weight body by pawl portion formed by caulking said opened. In U.S. Pat. No. 6,250,721 try to solve the problem by coupling the clip to the weight body of ductile casting iron by caulking head of the pillar. Those two patents have some defects leaved that two sides caulking point linearly to the guiding aperture, and the clip is coupling to the underside of the weight body, if there are some defects while caulking the cast-iron which will often causing crack in the metallic ground-boundary and causing broken afterward, sometimes even the clip hammer to the rim of the wheel, but the weight body will be loosed freely. Refer to our example test.